In 1869, Professor Leopold Trouvelot (1827–1895) brought gypsy moth egg masses from France to Medford, Massachusetts. His intention was to breed the gypsy moth (Porthetria dispar) with the silkworm to overcome a wilt disease of the silkworm. He placed the egg masses on a window ledge, and evidently the wind blew them away. About ten years later these caterpillars were numerous on trees in that vicinity, and in 20 years, trees in eastern Massachusetts were being defoliated. In 1911, a contaminated plant shipment from Holland also introduced the gypsy moth to Massachusetts.

Gypsy moths are now found throughout the entire northeastern United States and portions of Virginia, North Carolina, Ohio, and Michigan.

The gypsy moth lays its eggs on the leaves of oaks, birches, maples, and other hardwood trees. When the yellow hairy caterpillars hatch from the eggs, they devour the leaves in such quantities that the tree becomes temporarily defoliated. Sometimes this causes the tree to die. The caterpillars grow from 0.5 inch (3 millimeters) to about 2 inches (5.1 centimeters) before they spin a pupa, in which they will metamorphose into adult moths.